Synthesis, Photo- and Electroluminescence of New Polyfluorene Copolymers Containing Dicyanostilbene and 9,10-Dicyanophenanthrene in the Main Chain

Abstract

Using palladium-catalyzed Suzuki polycondensation, we synthesized new light-emitting fluorene copolymers containing the dicyano derivatives of stilbene and phenanthrene and characterized them by gel permeation chromatography, UV-vis absorption spectroscopy, spectrofluorimetry, and cyclic voltammetry. The photoluminescence spectra of the synthesized polymers show significant energy transfer from the fluorene segments to the dicyanostilbene and 9,10-dicyanophenanthrene units, which is in agreement with the data of theoretical calculations. OLEDs based on these polymers were fabricated with an ITO/PEDOT-PSS (35 nm)/p-TPD (30 nm)/PVK (5 nm)/light emitting layer (70–75 nm)/PF-PO (20 nm)/LiF (1 nm)/Al (80 nm) configuration. Examination of their electroluminescence revealed that copolymers of fluorene with dicyanostilbene show yellow-green luminescence, while polymers with 9,10-dicyanophenanthrene have a greenish-blue emission. The 9,10-dicyanophenanthrene units have a more rigid structure compared to dicyanostilbene and, in OLEDs based on them, an increase in maximum brightness is observed with an increase in the content of the additive to the polymer chain. In particular, the device using fluorene copolymer with 9,10-dicyanophenanthrene (2.5 mol%) exhibited a maximum brightness of 9230 cd/m2 and a maximum current efficiency of 3.33 cd/A.

Effect of Complexation with Closo-Decaborate Anion on Photophysical Properties of Copolyfluorenes Containing Dicyanophenanthrene Units in the Main Chain

“…All calculations were performed with the CAM-B3LYP functional [10]. It has been shown previously [8] that CAM-B3LYP better describes the phenanthrene molecule. To choose the most appropriate basis set, a comparative analysis of theoretically calculated spectra and experimental data was performed for each structure (B 10 H 9 − , PFCN-B1, PFCN-B2).…”

“…CPFs containing 0.5, 2.5, and 5% of 9,10-dicyanophenanthrene units (PFCN0.5, PFCN2.5, and PFCN5, respectively) were synthesized via a Suzuki-Miyaura cross-coupling reaction according to a procedure described previously [8]. Their structures were confirmed by 1 H NMR and FT-IR spectroscopy.…”

“…A similar pattern is observed in the emission spectra. The addition of one boron cluster (B 10 H 9 ) results in a shift (of 5 nm) to the red region (423 nm, Figure 4) relative to PFCN (417 nm [8]). The addition of the second boron cluster (B 10 H 9 ) shifts the maximum of the emission spectrum to 433 nm and an additional peak appears in the red region (at 563 nm).…”